As a preceding vehicle recognition apparatus is proposed for a vehicle. The apparatus radiates a transmission signal such as a light or millimeter wave signal over a predetermined angular range in the forward direction of the vehicle and, by detection of a reflected signal obtained as a result of reflection of the transmission signal, recognizes a preceding vehicle existing at a location away from the vehicle in the forward direction. This preceding vehicle recognition apparatus can be applied to a variety of apparatuses mounted on a vehicle. Typical application includes a apparatus which generates a warning when the distance between the vehicle and a preceding vehicle becomes short, and a apparatus which controls the speed of the vehicle so as to maintain the inter-vehicle distance between the vehicle and a preceding vehicle.
Such a preceding vehicle recognition apparatus is disclosed in JP 2002-181936A. In this conventional preceding vehicle recognition apparatus, a scanning laser radar measures a distance between the vehicle and a beam-reflecting body existing in a detection area. In the measurement processing, the scanning laser radar carries out a grouping process to put portions determined to be portions of the same body in a group in order to find not only the distance between the vehicle and a beam-reflecting body, but also the azimuth and size of the body. In the grouping process, portions that are located at the same distance and move in the same direction continuously along the time axis are regarded as portions of the same body.
In particular, the preceding vehicle recognition apparatus selects a beam-reflecting body with a small width among detected bodies and determines whether or not there is a possibility that a portion of the selected body is concealed behind another body existing closer to the vehicle than the selected body. By determining such possibility, the preceding vehicle recognition apparatus is capable of determining whether or not a beam-reflecting body newly appears in front of the vehicle as the other body existing closer to the vehicle moves in the transversal direction of the movements.
In the case of an example shown in FIG. 14, it is assumed a first preceding vehicle 201 is traveling in front of a vehicle having a laser radar 200 and a second preceding vehicle 202 is traveling on the diagonally forward left side of the first preceding vehicle 201. In this case, the laser radar 200 is capable of measuring a distance to left and right reflectors 201L and 201R on the rear face of the first preceding vehicle 201 and a distance only to a left reflector 202L on the rear face of the second preceding vehicle 202. Since a right reflector 202R on the rear face of the second preceding vehicle 202 is located at a position concealed behind the first preceding vehicle 201 when viewed from the vehicle, the laser radar 200 is not capable of measuring a distance to the right reflector 202R on the rear face of the second preceding vehicle 202.
Thus, assuming that the second preceding vehicle 202 probably having its portion concealed and existing at a location farther from the vehicle 200 has a predetermined width, the conventional preceding vehicle recognition apparatus determines whether or not a portion of the second preceding vehicle 202 is concealed behind the first preceding vehicle 201 closer to the vehicle by determining whether or not the right edge of the second preceding vehicle 202 pertains to a projection area on the second preceding vehicle 202. The projection area is computed with coordinates of left and right edges of the first preceding vehicle 201 taken as a reference.
By making use of reflectors provided on the left and right edges of the rear face of a preceding vehicle, the conventional apparatus detects the positions of the left and right edges of the rear face of the preceding vehicle. Since the reflectors each have a high reflectance in comparison with the vehicle body itself, reflected signals each having a high intensity can be obtained from the reflectors. Thus, normally, the positions of the left and right edges of the rear face of a preceding vehicle can be detected with a high degree of precision based on received signals representing signals reflected by the reflectors. Then, by linking the detected positions of the left and right edges of the rear face as positions varying with the lapse of time to form movement vectors, the locus of the preceding vehicle can be found.
However, when the reflectors are dirty or the preceding vehicle is traveling along a curved road, for example, it is difficult to detect the reflectors in some cases. In such cases, the conventional apparatus is no longer capable of detecting the positions of the left and right edges on sides of the rear face of the preceding vehicle. Thus, the preceding vehicle is mistakenly put in the same group as another preceding vehicle traveling in parallel to the preceding vehicle. It is therefore difficult to keep track of the movement or the locus of the preceding vehicle with a high degree of reliability.